In the past, there have been two principal methods and means for delivering a medicament within a body cavity, namely squeezable reservoir-type applicators and syringe-type applicators. The squeezable reservoir-type applicators suffer from several drawbacks in that they are often cumbersome, difficult to handle, imprecise at delivering a measured dosage, and inefficient because there is usually a significant amount of medicament remaining in the reservoir after use. Likewise, syringe-type applicators are typically somewhat bulky, difficult to use, and oftentimes inefficient in that a significant amount of medicament remains in the syringe after use.
The present invention pertains more to the syringe-type class of medicament applicators. These applicators have typically included a tubular reservoir with a delivery portion and closure at one end and a piston and rod (or plunger) at the other end. Following are some examples of syringe-type applicators of the past.
The U.S. Patent to Lorenian (U.S. Pat. No. 2,178,840) discloses a cylinder cut to have the shape of saw teeth at one end, which teeth are then bent toward the cylinder's central axis until they meet and thereby provide a closure, such that when acted on by pressure applied to dispense the medicament, the saw teeth part, clearing the way for the medicament.
U.S. Pat. No. 2,720,881 (to Jones) illustrates different forms of pressure-actuated, automatically-opening closures for the end of a medicament applicator. There, the closure is formed as part of a flat end of a crushable container held inside the applicator tube. The closures are varied designs of light incisions into the face of the flat end. These forms of closure are likely to be somewhat air-permeable, do not have the structural strength to serve as a contoured insertion tip for the applicator, and are subject to being accidentally opened.
A different form of disposable applicator is shown in another U.S. Patent to Jones (U.S. Pat. No. 2,691,982) wherein, for compactness purposes, the plunger is a hollow tube with a crimped end and an open end. The open end is disposed within the barrel of the applicator, surrounding a crushable thin-walled container at the delivery end of the applicator tube. For use, the plunger is removed, inverted, reinserted (crimped end first) into the tube and applied against the thin-walled collapsible container to expel the medicament through a discharge opening at the end of the applicator, which opening is forced open by the pressure of the medicament. This device is difficult to use, in that it involves disassembly and reassembly, and is not tapered for easy insertion. The closure portion suffers form the disadvantages discussed above with reference to U.S. Pat. No. 2,720,881.
The U.S. Patent to Huck (U.S. Pat. No. 3,506,008) provides a reservoir with a tapered dispensing end and a cap receivable over the tapered end to serve as a closure, requiring complicated internal threading to secure the closure in place. The cap is removable by twisting it off, and then must be inverted and inserted into the other, larger end of the dispenser, were it is used as a rod to drive a piston down the barrel of the applicator to expel the medicament contained therein. The Huck device likewise suffers from being difficult to use.
As a final example of prior applicators, in the U.S. Patent to Friedman, et al. (U.S. Pat. No. 2,072,327) a dispensing device is shown wherein a syringe has a piston with a rod disposed therethrough. An enlarged end of the rod mates with an opening at the delivery end of the syringe barrel and acts as a closure therefor. In use, the rod is drawn back, thereby opening the dispensing orifice, and pulled back towards the opposite end of the applicator, passing through the piston until the enlarged end of the rod comes into a locking engagement with the piston. So engaged, the rod can be used to move the piston through the syringe towards the dispensing end, thereby expelling the medicament. This device, while providing a reasonably compact medicament applicator, suffers from problems in sealing (to prevent moisture evaporation from the medicament) and apparently also from difficulty in use because the plunger stem resists being drawn back and does not have an easy-to-use grasping surface. The device would be difficult to prefill with medicament, and further, medicament appears likely to adhere to the sides of the rod when it is drawn back through the medicament in order to be set into the piston for discharge.
These disadvantages have all been overcome in the present invention, which can be described as having the following aspects.